1. Field of the Invention
This invention relates to an apparatus and method for the absorption of sound, radio and radiation waves. More particularly, this invention concerns the combination of a non-reflecting wave structure and a wave-absorbing portion.
2. Description of the Prior Art
Both sound waves and radio waves share the characteristic of being reflected upon contacting an object. In some instances, reflection of sound and radio waves from an object may be undesirable.
Sonar and radar are based on the reflection characteristic of sound and radio waves, respectively. A transmitter outputs a sound or radio wave pulse which contacts an object and is then reflected. A receiver is positioned to accept the reflected wave while observing the direction of the reflected wave and the amount of time it makes the wave to travel to and from the object. Thus, knowing the travel time of the wave and the speed of the wave, the position of the object can be determined. In the case of stealth submarines and stealth aircraft, it is desirable for the submarines and aircraft to be invisible to sonar and radar, respectively.
When sound waves contact an object the reflected waves can interfere with one another causing distortion of the sound waves. If constructive interference occurs, the sound waves reinforce one another to produce a resultant sound wave with increased intensity. If destructive interference occurs, the resultant sound wave will be of smaller intensity than the intensity of each of the interfering waves. Sound waves having different frequency and interfering with one another may result in beat which is heard as bursts of increased sound. Further, if the resultant wave frequency is at a natural frequency of a nearby body, unwanted vibration of the body can occur. In all of these instances, it may be advantageous to prevent distortion of the waves in order to maintain both purity of sound and structural integrity of nearby bodies.
The prior art prevents both distortion of waves and detection of objects using sonar and radar by attempting to absorb the waves before the waves are reflected from objects.
Prior art devices may utilize honeycomb panels and porous materials alone and in combination with one another to absorb and attenuate sound waves, Honeycomb panels composed of resonant chambers may be provided in ceiling structures, aircraft engines, and gas turbine engines in order to reduce noise and vibration. Sound waves passing through the resonant chambers are transformed into sound waves having different frequencies resulting in decreased noise and vibration.
Porous materials including fibrous structures may also be utilized in both ceiling panel and engine construction to absorb and attenuate sound waves. The sound waves move through the pores and encounter fibers which provide a frictfonal drag on the waves thus, converting the sound waves into heat which is released into the atmosphere. The porous material can be open-celled foam, fiberglass, mineral wool or felt.
The degree of sound absorption and sound attenuation can be increased by utilizing porous material in combination with honeycomb panels. Porous material can be provided within the resonant chambers of the honeycomb panels. Alternatively, the honeycomb panels and porous materials can be layered to form a sound attenuating panel.
Some prior art devices employ materials containing finely powdered carbon and iron to attenuate radio waves. Stealth Technology The Art of Black Magic, J. Jones, copyright 1989, discloses both ferrite-based coatings and polymer coatings containing carbon and being utilized as radar absorbing materials.
Each of the noted-prior art devices do not provide a non-reflecting wave structure being combined with a wave-absorbing portion.